Page Comparison

How does ideCAD calculate torsional strength according to ACI 318-19?

...

...

Notation

A_o = gross area enclosed by torsional shear flow path, in.²
A_oh = area enclosed by centerline of the outermost closed transverse torsional reinforcement, in.²
A_cp = area enclosed by outside perimeter of concrete cross section, in.²
A_g = gross area of concrete section, in²
A_l = total area of longitudinal reinforcement to resist torsion, in.²
A_l,min = minimum area of longitudinal reinforcement to resist torsion, in.²
A_t = area of one leg of a closed stirrup, hoop, or tie resisting torsion within spacing s, in.²
b_w = web width or diameter of circular section, in.
f_c^' ₌ specified compressive strength of concrete, psi
(f_c^')^0.5 ₌ square root of specified compressive strength of concrete, psi
f_{pc =} compressive stress in concrete, after allowance for all prestress losses, at centroid of cross section resisting externally applied loads or at junction of web and flange where the centroid lies within the flange, psi.
f_{yt =} specified yield strength of transverse reinforcement, psi
N_u = factored axial force normal to cross section occurring simultaneously with V_u or T_u; to be taken as positive for compression and negative for tension, lb
p_{cp =} outside perimeter of concrete cross section, in.
p_{h =} perimeter of centerline of outermost closed transverse torsional reinforcement, in.
s = center-to-center spacing of items, such as longitudinal reinforcement, transverse reinforcement, tendons, or anchors, in.
T_{cr =} cracking torsional moment, in.-lb
T_{th =} threshold torsional moment, in.-lb
T_{n =} nominal torsional moment strength, in.-lb
T_{u =} factored torsional moment at section, in.-lb
V_{u =} factored shear force at section, lb
ϕ = strength reduction factor
λ = modification factor to reflect the reduced mechanical properties of lightweight concrete relative to normal-weight concrete of the same compressive strength

...

Torsional design is made with the reinforcement requirement determined by comparing the factored torsional moment T_u value with the threshold torsion T_th and cracking torsion T_cr values.

• Torsional effects can be neglected if the factored torsional moment at section T_u is less than threshold torsion multiplied by strength reduction factor ϕT_th (T_u<ϕT_th). Torsional moments that do not exceed the threshold torsion T_th will not cause a structurally significant reduction in either flexural or shear strength and can be ignored.

• If T_u ≥ ϕT_cr it is assumed that closed stirrups, longitudinal bars, and compression diagonals provide the torsional resistance. Therefore, the reinforced concrete member is designed to resist T_u.

• If ϕT_cr > T_u ≥ ϕT_th, only minimum tension rebar needs to be provided ACI 9.6.4.

...

For the calculation of Torsional strength, it is assumed that the unit of (f_c^')^0.5 [or ] is psi. If these values are to be calculated in SI-metric or mks-metric units, the (f_c^')^0.5 [or ] value is changed accordingly.

...